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Billions of tiny life forms in the house called bacteria cover the tables and chairs and the floor

Peek into a clean room with no one
in it. There are no pets in the room. There are no plants in the room. It looks
like there is nothing alive in the room. The room, however, is swarming with
life. Billions of tiny life forms called bacteria cover the tables and chairs
and the floor. You can’t see them, but they stick to the windows, they cling to
the ceiling, and they float through the air. Bacteria constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a number of shapes, ranging from spheres to rods and spirals.Bacteria are tiny single-cell microorganisms, usually a few micrometers in length that normally exist together in millions. A gram of soil typically contains about 40 million bacterial cells. A milliliter of fresh water usually holds about one million bacterial cells.Bacteria as prokaryotes. All living organisms on Earth are made up of one of two basic types of cells: eukaryotic cells, in which the genetic material is enclosed within a nuclear membrane, or prokaryotic cells, in which the genetic material is not separated from the rest of the cell.
Suppose you looked at part of a
chair in the room through a microscope. Microscopes magnify bacteria. You would
see pale forms moving and bumping into each other like ghosts. These tiny life
forms are bacteria. They live everywhere in the world. Billions of them even
live inside of you!
Bacteria come in three basic
shapes. Some are round or shaped like a jellybean. Some are spiral-shaped like a
corkscrew. Some are long, like rods.
Each sphere or spiral or rod is
called a cell. Animals have millions of cells, but bacteria have only one cell.
This single bacterial cell is called a bacterium. An outer wall surrounds the
cell and protects it. A substance called DNA floats around inside the cell.
Some bacteria have hairlike parts
called flagella. The flagella help the bacteria move around in search of food.
Flagella also move bacteria away from things that could harm them.
Some bacteria help you. Bacteria
in the body help fight off disease and help you digest your food. Some bacteria
that live in soil help plants by producing substances plants need. They break
down dead plants and animals and animal waste. They make a gas called carbon
dioxide from decaying material. Other bacteria help plants take a gas called
nitrogen out of the air. Plants need carbon dioxide and nitrogen in order to
Some bacteria can harm you. There
are bacteria that cause food poisoning, pneumonia, tuberculosis, and other
sicknesses. Some bacteria cause tooth decay. Bacteria can also infect farm
animals and wild animals.
Disease-causing bacteria are
different from helpful bacteria. You can swallow disease-causing bacteria in
unclean food or water. Bacteria that cause infections can get into cuts and
sores. Bacteria can get on your hands and go from your hands into your nose,
eyes, or mouth. That is why it is so important to wash your hands often.
Most bacteria simply split in two.
Bacteria reproduce very rapidly. One bacterial cell can become two in just a few
minutes. Two bacteria become four bacteria and then four become eight bacteria.
Bacteria keep multiplying this way until there are billions of them.
Different kinds of bacteria must
compete for food. This competition keeps bacteria from overrunning Earth.
No one knew about bacteria until
the microscope was invented. Bacteria are so small that they must be magnified
at least 500 times their actual size for us to see them.
A Dutch microscope-maker named
Antoni van Leeuwenhoek in the 1670s was the first person to see bacteria under a
microscope. He saw tiny life forms swimming around in drops of rainwater and in
scrapings from his teeth. He called the bacteria “animalcules,” meaning tiny
French  Louis Pasteur in
the 1800s proved that some bacteria are germs that cause disease. He found that
heat kills bacteria. Heating surgical instruments to kill bacteria is called
sterilization. Heating milk and other foods to kill bacteria is called
pasteurization, a word named for Pasteur.
A German scientist named Robert
Koch also made important discoveries about bacteria. He founded a field of
called bacteriology, the study of bacteria.
Scientists study bacteria to find
out how these tiny life forms behave. Scientists also want to know what diseases
bacteria cause. They look for ways to kill disease-causing bacteria.
In the mid-1800s, scientists
learned that killing bacteria can stop the spread of some diseases. Doctors
learned that sterile surgical instruments and operating rooms help prevent
infection after operations. Scientists learned that having clean drinking water
and food prevents the spread of deadly diseases such as cholera and typhoid.
Scientists also learned how to
make vaccines that protect against some diseases caused by bacteria. They made
vaccines from dead or weakened bacteria or from poisons bacteria produce. For
example, a shot of tetanus vaccine protects you from the bacteria that cause
tetanus. Tetanus bacteria live in the soil. They can get into even small cuts on
your body. Tetanus causes muscles to tighten. It can be deadly.
In the mid-1900s, scientists
discovered antibiotics, drugs that kill bacteria. Before antibiotics, many
people died from pneumonia and other infections caused by bacteria. Some
bacteria have become resistant to antibiotics. The antibiotics no longer kill
them. Scientists are working to make new kinds of antibiotics that will kill
resistant bacteria.